The three sources of cellulose are boiled oak tree bark, oak leaves, and grated corncobs. I live in Oak Grove Apartments so I can goright outside and pick up the bark and the leaves, I've crumbled the leaves on top of different recipes and have ground both the bark and the leaves into a dry mix with other ingredients. The oak leaves are also a source of tannin, which brings out the hermies color. I found an article written for the Crab Street Journal entitled something like "How Old is My Crab?" One of the crabbers mentioned in Vanessa's article shared that she has raised two crabs for 11 years and there are pictures of them at various sizes. She regularly feeds her guys oak leaves and bark, and they are beautiful crabs. I have a feeling that adding cellulose to my crabs diet is a good thing to do. And these are ingredients I don't even have to pay for. YAY. I hope this helps. Thanks for letting me share, though I'm sorry I'm so long winded.